Tandem coil alternators have desirable properties for general automotive use and typically employ a rotor comprising an assembly of magnetically-permeable core pieces which surround and support two separate field coils. The two field coils are energized through slip rings positioned on the rotor shaft external to the core pieces. Alternators and generators using tandem field rotors generate more electrical energy at lower rotational speeds than conventional rotors of comparable size and weight, and offer a more desirable package shape for many applications since they have a smaller diameter relative to their length. The magnetic flux path for each field coil in a tandem field motor may be advantageously provided by a pair of core pieces having interleaved claws which surround the coil. An early tandem-field rotor of this type is described in U.S. Pat. No. 829,015 and a more recent design is described in U.S. Pat. No. 4,980,595.
A tandem field rotor must incorporate electrical interconnections between the slip rings and the field coils. It is an object of this invention to improve the reliability of such interconnections by making them a mechanically integral part of the rotor structure. It is a further object of the invention to obtain such a durable structure using fabrication methods which minimize labor and materials costs.
In a principal aspect, the present invention takes the form of an improved arrangement for interconnecting the windings and slip rings in the rotor of an alternator or the like. In accordance with the invention, sized passageways formed in the magnetic core pieces surround and rigidly support a pair of L-shaped electrical conductors which connect the coils to the two slip rings.
Insulating sleeves sized to conform to the core passageways separate the L-shaped conductors from the magnetic core structure. These sleeves include a pair of axially-extending tubes which support and surround the axial arm of each L-shaped conductor as that arm passes through the body of the magnetic cage structure. The radial arms of the two L-shaped conductors are embedded in a radial support member which is provided with a center hole through which the rotor shaft passes and which is shaped to conform to a retaining channel formed by recesses in the abutting faces of the interior core pieces.
According to a further feature of the invention, each field coil is wound on an insulating support bobbin. A pair of electrical contact terminals are attached to the bobbin and positioned to engage with and form an electrical connection to an exposed contact surface formed by the end of the radially-extending arm of each L-shaped conductor. Correspondingly, the end of the axially-extending arm of each L-shaped conductor extends beyond the end of the tube which insulates it from the core pieces to form further exposed contact surfaces to which the slip ring terminals may be readily connected during fabrication.